Here is the full list of all 75 Halo Wars: Definitive Edition achievements worth 1,500 gamerscore.
Finished all missions under Par Time on Heroic difficulty.
Finished five missions under Par Time on Heroic difficulty.
Won 100 Skirmish or Multiplayer Matches.
Completed the Campaign on Heroic Difficulty.
Completed the Campaign on Legendary Difficulty.
Won 75 Skirmish or Multiplayer Matches.
Won 50 Skirmish or Multiplayer Matches.
Got 20,000 points in any Skirmish Game.
100% Completion.
Finished with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Got a Scarab during a Reinforcement game.
Gained at Least 15 population from a single wave in a Reinforcement game.
Hot dropped 50 squads to your Covenant Leader in a single game on Barrens.
Killed 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Won 40 Skirmish or Multiplayer Matches.
Disrupted 5 active Leader Powers in a single game on Blood River.
Won and never trailed in a Tug of War game.
Used one of the 6 Major Leader Powers to destroy an enemy's last unit.
Won 30 Skirmish or Multiplayer Matches
Won and had the highest score in a Public Game.
Won a Skirmish Game with Dual Scarabs.
Got a Gold Medal on every Campaign Mission.
Got a Gold Medal with all Debuff Skulls Active.
Won a game on every Skirmish Map.
Unlocked All Timeline Events.
Won a 3v3 Skirmish game with 2 AI Allies.
Won 20 Skirmish or Multiplayer Matches
Mission 15: Opened the Doors in order.
Obtained a lifetime campaign Score over 1,000,000.
Completed Mission 15 on any difficulty.
Collected all Skulls.
Played Halo Wars for at least 24 Total hours.
Completed Mission 14 on any difficulty.
Mission 14: Didn't claim an extra base.
Completed Mission 13 on any difficulty.
Mission 13: Destroyed 25 units with the Scarab.
Mission 12: Repaired the Power Core in less than 4 minutes.
Completed Mission 12 on any difficulty.
Completed Mission 11 on any difficulty.
Mission 11: Saved all the Airlocks.
Completed Mission 10 on any difficulty.
Mission 10: Distrupted all Tractor Beams.
Completed Mission 9 on any difficulty.
Mission 9: Every Colony put in Hibernation Mode at the same time.
Completed Mission 8 on any difficulty.
Collected 8 Skulls.
Mission 8: Used Elephants to train 100 infantry.
Completed Mission 7 on any difficulty.
Mission 7: Did not destroy any Power Node.
Completed Mission 6 on any difficulty.
Mission 6: Successfully protected every Rhino.
Improved your Score in any Campaign Mission.
Completed Mission 5 on any difficulty.
Mission 5: Jacked 6 Covenant Vehicles.
Scored the winning point in a game of Keepaway against Legendary AI's.
Got a winning High Score with 10 or less Squads against the Heroic AI.
Won a Heroic Skirmish Game against the AI in under 10 minutes.
Won a Skirmish Game with every Leader.
Unlock 20 Timeline Events.
Won 10 Skirmish or Multiplayer Matches
Completed Mission 4 on any difficulty.
Mission 4: Saved Adam.
Completed Mission 3 on any difficulty.
Mission 3: Killed at least 5 Covenant Units with the Bridge.
Completed Mission 2 on any difficulty.
Mission 2: Destroyed every Methane Tank.
Mission 1: Rammed and killed 50 Grunts with Warthogs.
Finished one mission under Par Time on Heroic difficulty.
Collected your first Skull.
Got a Gold Medal on any mission.
Completed any Campaign Mission in Co-op Mode.
Completed Mission 1 on any difficulty.
Won a Public game.
Won a game in every Skirmish Game Mode.
Unlocked a Timeline Event.